In recent years, liquid crystal panels are in general use as the display part for televisions, mobile telephones, personal digital assistants, and the like. Liquid crystal panels cannot emit light on their own, and thus, in order to display images, light from an illumination device (the so-called backlight) is used. This illumination device is disposed on the rear surface side of the liquid crystal panel, and is configured so as to radiate light spread in a planar manner towards the rear surface of the liquid crystal panel.
As the illumination device, a type including a light guide plate and a light source unit disposed facing an edge face of the light guide plate is known (Patent Document 1, for example). This type of illumination device is generally known as the side light type (or edge light type), and as the light source unit, a light source unit constituted of a plurality of LEDs and an LED substrate upon which these LEDs are mounted is used, for example. As light from the respective LEDs mounted on the LED substrate is radiated towards a side edge face of the light guide plate, this light enters the light guide plate at the side edge face, and travels inside the light guide plate while being reflected by a reflective sheet or the like disposed below the light guide plate. This light is outputted as planar light from the front surface of the light guide plate. The light emitted from the front surface of the light guide plate passes through optical sheets made of a transparent resin and disposed on the front surface of the light guide plate, and illuminates the liquid crystal panel from the rear thereof. The size of the optical sheets is generally set such that the front surface of the light guide plate can be covered.